Reading pot codes

How to read pot codes, and what they mean

An early 1960s pot from a Gibson guitar. Once decoded, the writing on the back or sides can be very informative

If you've been reading articles about dating a vintage guitar, you may well have come across mention of pot codes. The pots, or potentiometers to give their full name, are the variable resistors that control volume and tone. Better quality pots are often stamped with a number of codes; typically part numbers, date of production, manufacturers codes and resistance values. Many pots don't carry all of this information, but the better quality guitars produced in America regularly do.

So where are these codes? Normally they are stamped or inked onto the back or sides of the pot. So reading them will require opening control cavities, removing scratchplates, or in the case of a semi acoustic, removing the pots entirely. Codes can be worn, obscured by solder and other components, or simply very small. Finding them is not always easy; this is obviously not something for the faint-hearted, but once performed a few times, nowhere near as daunting as it might at first seem. There are many exceptions and variations to the general rules described below, some of which are highlighted in the examples at the end.

Part numbers

Many pots do not have part numbers, but the larger guitar manufacturers did list pots by part number in their spare parts manuals. You can look up Gibson potentiometers by their part number in the Gibson pot index on this site.

Manufacturers codes

There are very many electronic companies worldwide producing potentiometers, but most American vintage guitars of the 20th Century used pots by just a few manufacturers. American pot manufacturers had their own numerical codes, for example 134 = Centralab, 137 = CTS and 304 = Stackpole. Although many others were used, these are by far the most important, as they were widely used by the likes of Gibson, Fender, Guild and Epiphone. Other worldwide manufacturers just used the company name rather than a code. Many also put a country of production.

Production dates

Production dates are usually in three or four digits, one or two digits giving the year (for many US pots one digit refers to the 1950s, two digits to the 1960s), and two giving the week of the year. These often run on from the manufacturer code. For example 1346120 is a centralab pot (134) produced in the 20th week of 1961. But remember this is the date that the potentiometer was produced. Pots in an older guitar may have been replaced, and this should be considered, especially if the date suggested does not fit with other features of the guitar. What's more, guitar companies sometimes took a very long time to use the potentiometer in question, and they may be considerably older than the guitar itself. Fender, famously bought huge stocks of pots in 1966, and took almost a decade to use them all. Conversely, guitars were also built, but not wired and shipped immediately, resulting in newer pots in older guitars. This is especially the case for guitars that were only ever shipped in tiny numbers. Pot dates are a useful tool in dating a guitar, but should always be used in conjunction with other known factors, such as hardware changes and serial numbers.

Resistance values and taper

Resistance values are normally listed. 250k, 500k and 1 Meg (1000k) being the most common. The taper of a pot describe how the resistance changes with the turning of the pot. The words LIN on a pot means a linear taper; turned half way, the resistance is at approx. 50% of maximum, three quarters of the way at 75% of maximum etc. AT stands for audio taper. These change logarithmically.

Examples

1961 Centralab pot as fitted to an early Gibson SG Special. In this case the codes are stamped in very small font to the side of the pot casing.1346120 (Centralab pot, 20th week of 1961)BA811-1053 (Gibson part number 811-1053)500k (resistance value)

The volume pot of a 1963 Hofner President bass. These early Hofner pots have very little information; a resistance value of 250k and 383 - in this case meaning week 38 of 1963. These appear on the underside of the pot.

This early 1960s British pot came from a UK built Vox Shadow. It has little information on it: UK 500K LIN (a resistance value of 500k, a linear taper, and the fact that it was made in the UK). The manufacturer's name, Morganite is there, but no means of dating. Morganite were based in Jarrow, Tyne and Wear

Many Vox guitars were made by Eko in Italy, and these used Italian pots. Again they have little information. This one (from a late 1960s Vox Astro bass) is marked LESA, made in Italy on the back, with 500k 1 22 on the side. Again dating does not seem to be possible with these pots. Guitars by Vox, Eko and Hagstrom all used Lesa potentiometers.

1969 CTS pots as fitted to a 1969 Gibson Melody MakerTX1158 (Gibson part number) 500k AT (resistance value, audio taper)One has a code of 1376902 (CTS pot, 2nd week of 1969), another has 1376852 (CTS pot, 52nd week of 1968)

Stackpole pot as fitted to a 1971 Fender Telecaster. Fender Centralab and CTS pots, but used Stackpole widely in the late 1960s and early 1970s.032367 (Fender part number)250K (resistance value)304-7116 (Stackpole pot, 16th week of 1971)

1973 CTS pot as fitted to a Fender Musicmaster bass. Note this is the same part number as the 1971 Stackpole pot above, although now produced by CTS.032367 (Fender part number, obscured)250K (resistance value)1377329 (CTS pot, 29th week of 1973)

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Martyn Comment left 14th August 2017 11:11:24 replyHello, I have an old Hofner which could be a model 4572E2. The volume pot needs replacing and I can't as yet, find a direct replacment. The numbers on the side read - 478 250k not sure if the fist 3 digits are the date? Any ideas?

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Ron Watkins Comment left 10th April 2016 20:08:00 replyI recently purchased a 1964 Hofner 500/1 with the narrow control panel. The numbers on the pots read 250K 923 Does anyone know what 923 says about the date? I thought the first two numbers signified the week and the last number the year..obviously that couldn't apply here. I thought the "3" indicated the pots were 1963, but can't make sense of the "92". Would appreciate any help. Thanks!

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Alex Comment left 10th April 2016 20:08:55 replywho done the soldering on these pots : what a mess :

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carl thomas Comment left 8th May 2015 21:09:56 replyHello i have a grestch streamliner guitar . the sticker is gone the pot code is 885p601, any idea what year it is < Thanks, Carl

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Joe Comment left 5th December 2014 07:07:22 reply I've got two pots here from a lap steel harness (bakelite) that has two sets of numbers on the pot.
here they are: NM6482 and R9043, both these numbers are on each pot.
any help would be greatly appreciated, thanks

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vic Comment left 8th November 2014 22:10:29 replyI was just trying to look up centralab on the net to id this potentiometer and found your site.
Looks like i have a #1347228 then a space
-1080 space 500k-c1 measures out to 444k ohm pretty sure this isn't for a guitar but maybe a amp??
was going to use this for a jury rig because i do not have a 1mohm on hand.